The purpose of this core is to develop a model program for the genetic counseling and testing of Alzheimer patients and their families. Recent genetic advances have expanded our knowledge about the genetics of Alzheimer disease (AD) and the genetic testing options for patients and their families. Previous evidence of the involvement of chromosome 19 in late onset AD has been confirmed by the finding of a significant association between AD and the apolipoprotein E (Apo-E) locus. Research has also shown that 1-antichymotrypsin (ACT) may confer a significant risk for AD as well as active conjunction with ApoE. Three major genes accounting for up to 90% of early onset autosomal dominant AD have also been discovered. Genetic testing for AD may prove beneficial to millions of individuals affected by, or at risk for, AD. For affected individuals, testing for the combination of ApoE/ACT may help in clarifying the diagnosis of AD and in choosing treatment options. For persons at risk for early onset AD, predictive genetic testing is now possible with a high degrees of accuracy. What is unknown, however, is the response of this group of consumers to these new options. Genetic counseling will be offered to all patients and their families. Patients diagnosed with probable or possible AD will be tested for ApoE/ACT as part of their basic workup in the clinical core. Presymptomatic testing of individuals at risk for AD will be initiated following a protocol adapted from those developed for Huntington disease. This protocol will include genetic counseling, psychological screening, pretest counseling and followup.